/*

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 *

 */

//

// Prioritized queue of VM operations.

//

// Encapsulates both queue management and

// and priority policy

//

class VMOperationQueue : public CHeapObj {

 private:

  enum Priorities {

     SafepointPriority, // Highest priority (operation executed at a safepoint)

     MediumPriority,    // Medium priority

     nof_priorities

  };

  // We maintain a doubled linked list, with explicit count.

  int           _queue_length[nof_priorities];

  int           _queue_counter;

  VM_Operation* _queue       [nof_priorities];

  // we also allow the vmThread to register the ops it has drained so we

  // can scan them from oops_do

  VM_Operation* _drain_list;

  // Double-linked non-empty list insert.

  void insert(VM_Operation* q,VM_Operation* n);

  void unlink(VM_Operation* q);

  // Basic queue manipulation

  bool queue_empty                (int prio);

  void queue_add_front            (int prio, VM_Operation *op);

  void queue_add_back             (int prio, VM_Operation *op);

  VM_Operation* queue_remove_front(int prio);

  void queue_oops_do(int queue, OopClosure* f);

  void drain_list_oops_do(OopClosure* f);

  VM_Operation* queue_drain(int prio);

  // lock-free query: may return the wrong answer but must not break

  bool queue_peek(int prio) { return _queue_length[prio] > 0; }

 public:

  VMOperationQueue();

  // Highlevel operations. Encapsulates policy

  bool add(VM_Operation *op);

  VM_Operation* remove_next();                        // Returns next or null

  VM_Operation* remove_next_at_safepoint_priority()   { return queue_remove_front(SafepointPriority); }

  VM_Operation* drain_at_safepoint_priority() { return queue_drain(SafepointPriority); }

  void set_drain_list(VM_Operation* list) { _drain_list = list; }

  bool peek_at_safepoint_priority() { return queue_peek(SafepointPriority); }

  // GC support

  void oops_do(OopClosure* f);

  void verify_queue(int prio) PRODUCT_RETURN;

};

//

// A single VMThread (the primordial thread) spawns all other threads

// and is itself used by other threads to offload heavy vm operations

// like scavenge, garbage_collect etc.

//

class VMThread: public NamedThread {

 private:

  static ThreadPriority _current_priority;

  static bool _should_terminate;

  static bool _terminated;

  static Monitor * _terminate_lock;

  static PerfCounter* _perf_accumulated_vm_operation_time;

  void evaluate_operation(VM_Operation* op);

 public:

  // Constructor

  VMThread();

  // Tester

  bool is_VM_thread() const                      { return true; }

  bool is_GC_thread() const                      { return true; }

  // The ever running loop for the VMThread

  void loop();

  // Called to stop the VM thread

  static void wait_for_vm_thread_exit();

  static bool should_terminate()                  { return _should_terminate; }

  static bool is_terminated()                     { return _terminated == true; }

  // Execution of vm operation

  static void execute(VM_Operation* op);

  // Returns the current vm operation if any.

  static VM_Operation* vm_operation()             { return _cur_vm_operation;   }

  // Returns the single instance of VMThread.

  static VMThread* vm_thread()                    { return _vm_thread; }

  // GC support

  void oops_do(OopClosure* f, CodeBlobClosure* cf);

  // Debugging

  void print_on(outputStream* st) const;

  void print() const                              { print_on(tty); }

  void verify();

  // Performance measurement

  static PerfCounter* perf_accumulated_vm_operation_time()               { return _perf_accumulated_vm_operation_time; }

  // Entry for starting vm thread

  virtual void run();

  // Creations/Destructions

  static void create();

  static void destroy();

 private:

  // VM_Operation support

  static VM_Operation*     _cur_vm_operation;   // Current VM operation

  static VMOperationQueue* _vm_queue;           // Queue (w/ policy) of VM operations

  // Pointer to single-instance of VM thread

  static VMThread*     _vm_thread;

};